A rib waveguide structure such as that shown schematically in FIG. 1 is a partially etched waveguide in which light is guided by a raised portion on a relatively wide slab waveguide. Such a rib waveguide allows for a reduced lateral index contrast and is advantageously employed in silicon photonics to make low-loss waveguides, waveguide crossings, directional couplers, adiabatic couplers and other structures. Notwithstanding, the slab waveguide in such structures guides much of the light that is scattered from the rib waveguide and which may later couple back into the rib waveguide, photo detectors, or other waveguides thereby degrading photonic integrated circuit (PIC) performance. Accordingly, improvements to such structures would represent a welcome addition to the art.